Compost Tunnel & Bunker Capacity Calculation
Sizing a Phase-1 bunker and Phase-2 pasteurisation tunnel: compost per grow room, tonnes per cycle, aeration rate and cycle-day planning.
How much compost does one mushroom grow room need?
Compost demand is driven by bag count: MushroomWale rooms carry 1,000 bags (18×30 ft) up to 3,000 bags (18×70 ft), and standard commercial bags hold roughly 25–30 kg of Phase-III compost each. A four-room farm therefore consumes tens of tonnes per cycle, which is what fixes bunker and tunnel size — not the farm's floor area.
Estimate your own numbers
Pick a room size and count — the tool applies the same engineering constants used in MushroomWale BOQs and returns a recommended plan summary.
Total built-up area
~1,440 sq ft
720 sq ft per room
Cooling requirement
~16 TR
8 TR per room
Bag capacity
~3,200 bags
1,600 bags per room
Phase-III compost
~80–96 T
per full filling (25–30 kg/bag)
MS racking material
~4,100 kg angle
+ ~450 kg jali (incl. wastage)
PUF doors
2 nos.
insulated cold-room doors
Yield per cycle
~6,400 kg
~106 kg/day at peak flush
Annual yield @ 5 cycles
~32,000 kg
fresh weight, all flushes
Recommended plan summary
Climate unit per room: Daikin 8 TR (~28 kW Outdoor Unit)
2× Outdoor Unit (4 HP ea., R32 3ph HMT) + 1× Indoor Unit (HMT Dual-Circuit Evap, 550mm fan)
Compost planning: ~80–96 tonnes of Phase-III compost per filling, staggered across rooms so tunnel turns stay continuous.
Indicative engineering estimate only — not a price quotation. Final sizing depends on site conditions, climate zone, ceiling height and grower practice. GST and transportation are extra; any additional client requirement is charged extra.
How MushroomWale calculates it
- 1
Start from total bag count per filling
Multiply bags per room by the number of rooms filled in one batch. Rooms are normally filled in a staggered sequence so the compost unit runs continuously instead of peaking.
- 2
Convert bags to tonnes of Phase-III compost
At roughly 25–30 kg of finished compost per bag, 2,500 bags is about 62–75 tonnes for a single 18×60 ft room filling.
- 3
Work backwards through the phases
Phase III output is less than Phase II input, which is less than raw wet-mix input. Size the bunker on raw mix, the tunnel on Phase-II charge weight, and never on the finished tonnage.
- 4
Match tunnel cycle days to room fill schedule
A standard 20 T or 30 T unit runs a roughly 15-day composting cycle. Your room filling calendar has to line up with tunnel turns; a mismatch means either idle rooms or compost with nowhere to go.
- 5
Size aeration to the charge, not to the room
Bunker and tunnel blowers are selected against charge weight and bed depth. Standard MushroomWale units use 3.5 HP × 2 (bunker) and 7.5 HP (tunnel) at 20 T, and 5 HP × 2 with a 10 HP tunnel blower at 30 T.
Reference data
Standard compost unit configuration
| Capacity | Bunker blower | Tunnel blower | Cycle |
|---|---|---|---|
| 20 tonne | 3.5 HP × 2 | 7.5 HP × 1 | ≈ 15 days |
| 30 tonne | 5 HP × 2 | 10 HP × 1 | ≈ 15 days |
20 tonne
- Bunker blower
- 3.5 HP × 2
- Tunnel blower
- 7.5 HP × 1
- Cycle
- ≈ 15 days
30 tonne
- Bunker blower
- 5 HP × 2
- Tunnel blower
- 10 HP × 1
- Cycle
- ≈ 15 days
Compost demand by room (indicative, at 25–30 kg finished compost per bag)
| Room | Bags | Phase-III compost per filling |
|---|---|---|
| 18×30 ft | 1,000 | ≈ 25–30 tonnes |
| 18×40 ft | 1,600 | ≈ 40–48 tonnes |
| 18×60 ft | 2,500 | ≈ 63–75 tonnes |
| 18×70 ft | 3,000 | ≈ 75–90 tonnes |
18×30 ft
- Bags
- 1,000
- Phase-III compost per filling
- ≈ 25–30 tonnes
18×40 ft
- Bags
- 1,600
- Phase-III compost per filling
- ≈ 40–48 tonnes
18×60 ft
- Bags
- 2,500
- Phase-III compost per filling
- ≈ 63–75 tonnes
18×70 ft
- Bags
- 3,000
- Phase-III compost per filling
- ≈ 75–90 tonnes
- Civil work for the compost yard, bunker and tunnel shell is client scope; MushroomWale supplies the engineering, equipment and commissioning.
- Bag fill weight varies with compost moisture and grower practice — verify against your own filling records before finalising a tunnel size.
Frequently asked questions
Related engineering pages
Talk to a MushroomWale engineer
Send your question on Compost Tunnel & Bunker Capacity Calculation and our project engineer will verify the sizing for your site — no cost, no obligation.
Want these numbers applied to your own site?
Share your plot size and target capacity — our engineers return a sized BOQ with room, machine and compost figures.
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